In general, a printed circuit board (PCB) is a component in which electric wirings are integrated to allow various devices to be populated therein or to be electrically connected to one another. Technological developments have led to an increase in production of PCBs having various forms and functions. Demand for such PCBs has been increasing with a growth of industries using the PCBs and relating to, for example, home appliances, communication devices, semiconductor equipment, industrial machinery, and electrical control of vehicles. In addition, PCB products are being transformed into a miniaturized, light-weight, and high value-added products, as electronic components become smaller and more sophisticated. As electronic components become increasingly more sophisticated and perform more complex functions, they consume increasing amounts of power, and, as a result, correspondingly generate greater amounts of heat. The levels of generated heat are such that they are becoming a factor used by consumers to evaluate a degree of satisfaction with the electronic product, and affect consumer purchasing habits.
Conventionally, a multilayer PCB is manufactured by using a copper-clad laminate (CCL) as a base substrate, forming a circuit pattern on the CCL, and laminating a layer. The use of copper (Cu) as a material for the base substrate which providing excellent conductivity, also limits the ability to improve heat dissipation characteristics of the PCB. When multilayer PCBs are required in an application, the conventional method of manufacturing with copper (Cu) becomes limiting, because of the resulting heat generated by the multilayer PCB.
Recently, developments have been made to manufacture PCBs using aluminum (Al) rather than copper (Cu), because aluminum (Al) has a more desirable thermal conductivity than copper (Cu).
Korean Patent Application No. 10-0674321 discloses an example of a PCB having aluminum as a base substrate. The PCB includes an aluminum core, a circuit pattern formed therein, a central layer having an etching resist pattern formed on opposite surfaces thereof, an insulation layer on opposite surfaces of the central layer, an additional circuit layer on the insulation layer and having a circuit pattern formed thereon, a through-hole penetrating the aluminum core, the insulation layer, and the additional circuit layer, and a zinc plating layer on an inner wall of the through hole, and a copper plating layer on the substrate that electrically connects the layers together.
Japanese Patent Publication No. 2004-179291 discloses a method of substituting aluminum for an insulation layer and forming a circuit on opposite surface to improve a bending reinforcing performance. The method includes preparing a desired surface roughness on a non-conducting material using through-hole treatment, closely contacting anodized aluminum to a plating layer in the through-hole, and forming a circuit on both aluminum faces. In addition, a desirable anodizing depth is disclosed having a range of 10 to 100 micrometers (μm), where no electrical shock occurs, and a desirable insulating function is achieved in an anodizing depth of 30 μm.
One of the disadvantages to the conventional methods of manufacturing a printed circuit board (PCB) using an aluminum core is that a surface of the aluminum core may be corroded during electroless copper plating. This is because an aluminum material included in the aluminum core of the PCB has a lower chemical resistance compared to conventionally used copper. In such a case, a copper film formed during the electroless copper plating may not be in a complete contact with a lower portion of the aluminum core, and a surface of the copper film is lifted, resulting in poor adhesion to the aluminum core after electrolytic copper plating has been performed. Thus, reliability of the resulting product decreases.
When used for office automation equipment, portable terminals, and the like having a relatively stable temperature range for application, the PCB manufactured using such a conventional technology may have a stable adhesion to the copper film due to the anodizing performed on the aluminum core. However, when applied to applications such as electronic controls for a vehicle or an engine room, the PCB suffers from decreasing adhesion between a thin aluminum film and the copper film due to the harsh environment.
In addition, when being applied to a vehicle, the PCB may have an issue in that the PCB may be damaged by a difference in a thermal expansion coefficient between the aluminum core and subsequent layers disposed on the aluminum core, due to high temperature typically found in such applications.
Further, the method of layering an insulator on both sides of a semi-processed aluminum substrate disclosed in Korean Patent Application No. 10-0674321 has other disadvantages. For example, the aluminum substrate is connected to subsequent layers due to a circuit etching process and thus, an independent portion or circuit may not be formed. In addition, an entire layer is limited to a certain electrode, (+) or (−), when applying an electric current. Thus, a great number of process steps are required to manufacture a multilayer PCB, and it is difficult to integrate the circuit and simplify the product.